<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>外间距测试</title>
    <style>
        .fu {
            background-color: #ff0;
            /*解决父元素与第一个子元素上边重合的问题*/
            overflow: hidden;
        }
        .fu>div {
            width: 100px;
            height: 100px;
            border: 5px solid #f00;
        }
        .z2 {
            margin-top: 50px;
        }
        .z1 {
            margin-top: 50px;
        }
    </style>
</head>
<body>
    <div class="fu">
        <div class="z1"></div>
        <div class="z2"></div>
        <div class="z3"></div>
    </div>
</body>
</html>